This invention relates to an altitude compensating system of a carburetor mounted on a vehicle, especially to an altitude compensating system which can vary the operating characteristics of a carburetor for obtaining a desirable enriched air fuel ratio in accordance with changes in altitude.
In conventional carburetors, the air fuel ratio is enriched for obtaining increased engine power when the throttle valve of the carburetor is opened. Furthermore, since the conventional carburetors, especially fixed venturi carburetors, mix a certain volume of air with a certain volume of fuel, when a vehicle which has the conventional carburetor mounted thereon is at high altitude, due to the decrease of the atmospheric pressure (and the specific weight of air), the total amount of intake air in weight is decreased, and the air fuel ratio at a given throttle setting is enriched. As a result, harmful contaminants, such as carbon monoxide (CO) and hydro carbon (HC) contained in exhaust gas emitted from the engine are increased and an engine power drop is caused. In addition, since the throttle valve is frequently opened due to the engine power drop at high altitude, the harmful CO and HC contaminants contained in the exhaust gas emitted from the engine can be further increased.